AU2022423803A1

AU2022423803A1 - Method for producing lithium hydroxide

Info

Publication number: AU2022423803A1
Application number: AU2022423803A
Authority: AU
Inventors: Satoshi Asano; Shin-ichi HEGURI; Yusuke SENBA; Masatoshi Takano
Original assignee: Sumitomo Metal Mining Co Ltd
Current assignee: Sumitomo Metal Mining Co Ltd
Priority date: 2021-12-22
Filing date: 2022-12-13
Publication date: 2023-07-20
Also published as: WO2023120294A1; JP2023092624A; CL2023002828A1; AU2022423803A9; EP4257552A1; AR128042A1

Abstract

To provide a method for producing lithium hydroxide allowing obtaining high purity lithium hydroxide by reducing impurities to a preliminarily determined level in a step before a conversion step by electrodialysis. The method for producing lithium hydroxide includes steps (1) to (5) below: (1) a hydrocarbonating step of blowing carbon dioxide to a slurry of a mixture of water and rough lithium carbonate; (2) a decarbonation step of heating a lithium hydrogen carbonate solution; (3) an acid solution dissolution step of dissolving a purified lithium carbonate in an acid solution; (4) an impurity removal step of removing a part of metal ions from a first lithium containing solution; and (5) a conversion step of converting lithium salt contained in a second lithium containing solution into lithium hydroxide by electrodialysis. This producing method allows reliably removing metals other than lithium, thereby allowing an increased purity of obtained lithium hydroxide. [Selected Drawing] Fig. 1 27

Description

METHOD FOR PRODUCING LITHIUM HYDROXIDE BACKGROUND

1. Technical Field

[0001]

The present invention relates to a method for producing lithium hydroxide.

More specifically, the present invention relates to a method for producing lithium

hydroxide including a conversion step by electrodialysis.

2. Related Art

[0002]

Recently, as a positive electrode material for an on-vehicle battery, demand for

a nickel-based positive electrode material, that is, NCA is expanding. Then, when the

nickel-based positive electrode material is used for the on-vehicle battery, it is

economically preferred that lithium as a constituent element of the nickel-based positive

electrode material is supplied as lithium hydroxide. This lithium hydroxide is obtained

by, for example, adding slaked lime to lithium carbonate to substitute a hydroxyl group.

Masao Kobayashi, Lithium, its History, Source, Production, and Application, Journal of

the Mining Institute of Japan, Japan, 1984, volume 100 issue 1152, 115-122 discloses a

method for obtaining lithium hydroxide from lithium carbonate. A reason why the

lithium carbonate is used as a starting material is that it is less likely to degenerate

compared with other lithium compounds, and can be stored for a long time. However,

this producing method for obtaining the lithium hydroxide from the lithium carbonate

has a problem of an increased production cost due to a high cost of agents. In addition,

there is also a problem of a high calcium concentration in the lithium hydroxide.

[0003]

Patent Document 1 discloses a method that uses electrodialysis (membrane

separation) and ion-exchange resin as a method for producing lithium hydroxide from

lithium carbonate. This method discloses that polyvalent metals with a valence of two

or more, such as calcium described above, can be reduced.

[0004]

Patent Document 1: JP-A-2009-270189

[0005]

Non-Patent Document 1: Masao Kobayashi, Lithium, its History, Source, Production,

and Application, Journal of the Mining Institute of Japan, Japan, 1984, volume 100

issue 1152, 115-122

[0006]

With the producing method in JP-A-2009-270189, an effect of removing

sodium and potassium, which are alkali metals the same as lithium, is limited because

the sodium and the potassium present a behavior similar to that of the lithium. In view

of this, when a sodium concentration in lithium carbonate as a raw material is high, a

purity of obtained lithium hydroxide lowers, thus failing to be used as a raw material for

a battery in some cases. In particular, when the lithium carbonate is produced using a

salt lake brine as a raw material, sodium hydroxide is used for a neutralizer for

removing impurities, which tends to increase sodium in the lithium carbonate, and in

this case, it is difficult to produce the high purity lithium hydroxide.

[0007]

Additionally, when concentrations of the polyvalent metals with a valence of

two or more, such as calcium, in an electrolyte are increased in the electrodialysis, a

used barrier membrane is easily damaged. There is a problem that the respective

concentrations of the polyvalent metals, such as calcium, in the electrolyte need to be less than 0.05 mg/L before the electrodialysis is performed in order to reduce this damage.

[0008]

In consideration of the above-described circumstances, it is an object of the

present invention to provide a method for producing lithium hydroxide allowing

obtaining high purity lithium hydroxide by reducing impurities to a preliminarily

determined level in a step before a conversion step by electrodialysis.

SUMMARY

[0009]

A method for producing lithium hydroxide according to a first invention

includes steps (1) to (5) below: (1) a hydrocarbonating step of blowing carbon dioxide

to a slurry of a mixture of water and rough lithium carbonate to obtain a lithium

hydrogen carbonate solution; (2) a decarbonation step of heating the lithium hydrogen

carbonate solution to obtain a purified lithium carbonate; (3) an acid solution

dissolution step of dissolving the purified lithium carbonate in an acid solution to obtain

a first lithium containing solution; (4) an impurity removal step of removing a part of

metal ions from the first lithium containing solution to obtain a second lithium

containing solution; and (5) a conversion step of converting lithium salt contained in the

second lithium containing solution into lithium hydroxide by electrodialysis to obtain a

lithium hydroxide containing solution in which the lithium hydroxide is dissolved.

The method for producing lithium hydroxide according to a second invention,

which is in thefirst invention, includes a crystallization step of solidifying the lithium

hydroxide dissolved in the lithium hydroxide containing solution after the conversion

step.

In the method for producing lithium hydroxide according to a third invention,

which is in the first invention or the second invention, the impurity removal step

includes: a pH adjustment step of adjusting a pH by adding alkali to the first lithium

containing solution to obtain a post-pH adjustment liquid; and an ion exchange step of

bringing the post-pH adjustment liquid into contact with ion-exchange resin to obtain

the second lithium containing solution.

In the method for producing lithium hydroxide according to a fourth invention,

includes: a step of adding an oxidant to the first lithium containing solution to obtain a

post-oxidation liquid; a pH adjustment step of adjusting a pH by adding alkali into the

post-oxidation liquid to obtain a post-pH adjustment liquid; and an ion exchange step of

the second lithium containing solution.

In the method for producing lithium hydroxide according to a fifth invention,

which is in the third invention or the fourth invention, the pH of the post-pH adjustment

liquid after the pH adjustment step is 6 or more and 10 or less.

In the method for producing lithium hydroxide according to a sixth invention,

which is in any one of the third invention to thefifth invention, the alkali includes

lithium carbonate or lithium hydroxide.

In the method for producing lithium hydroxide according to a seventh

invention, which is in the sixth invention, the lithium carbonate is the purified lithium

carbonate obtained in the decarbonation step.

In the method for producing lithium hydroxide according to an eighth

invention, which is in any one of the first invention to the seven invention, in the

decarbonation step, the lithium hydrogen carbonate solution is heated at 60C or more and 90C or less.

[0010]

According to the first invention, executing the hydrocarbonating step, the

decarbonation step, and the acid solution dissolution step in the step before the

conversion step by electrodialysis allows reliably removing the metals other than

lithium, and therefore, a purity of the obtained lithium hydroxide can be increased.

Additionally, the concentrations of polyvalent metals with a valence of two or more,

such as calcium, in the electrolyte can be lowered, and therefore, a damage of a barrier

membrane used in the conversion step after these steps can be reduced.

According to the second invention, the crystallization step of solidifying the

lithium hydroxide is provided after the conversion step, and therefore, the lithium

hydroxide can be solidified to have a high purity using a difference in solubility.

According to the third invention, the impurity removal step includes the ion

exchange step of using the ion-exchange resin and the pH adjustment step of adding the

alkali before the ion exchange step, and therefore, the pH can be adjusted to be

appropriate for the subsequent ion exchange step in the pH adjustment step and a

removal rate of divalent or more metals is substantially improved in the ion exchange

step.

According to the fourth invention, the impurity removal step includes the ion

exchange step of using the ion-exchange resin, and the oxidation step of adding the

oxidant and the pH adjustment step of adding the alkali before the ion exchange step,

and therefore, manganese can be removed when the manganese is contained in the first

lithium containing solution, and the pH can be adjusted to be appropriate for the

subsequent ion exchange step in the pH adjustment step, thereby substantially

improving a removal rate of divalent or more metals in the ion exchange step.

According to the fifth invention, the pH of the post-pH adjustment liquid after

the pH adjustment step is 6 or more and 10 or less, and therefore, the impurities are

removed with more certainty in the ion exchange step after the pH adjustment step.

According to the sixth invention, the alkali contains the lithium carbonate or

lithium hydroxide, and therefore, the added alkali can be avoided from being added with

impurities, such as sodium or potassium.

According to the seventh invention, the lithium carbonate is the purified

lithium carbonate obtained in the decarbonation step, and therefore, the use of the

product obtained in the previous step allows saving an extra cost.

According to the eighth invention, the heating is 60°C or more and 90°C or

less, and therefore, a process period in the decarbonation step can be shortened.

BRIEF DESCRIPTION OF DRAWINGS

[0011]

Fig. 1 is a flowchart of a method for producing lithium hydroxide according to

a first embodiment of the present invention;

Fig. 2 is a detailed flowchart of an impurity removal step of the method for

producing lithium hydroxide in Fig. 1;

Fig. 3 is a detailed flowchart of an impurity removal step constituting a method

for producing lithium hydroxide according to a second embodiment of the present

invention; and

Fig. 4 is a graph illustrating a relation between an energizing time in a

conversion step and a lithium concentration in a lithium hydroxide containing solution.

DETAILED DESCRIPTION

[0012]

Next, embodiments of the present invention will be described based on the

drawings. However, the embodiments described below are to exemplarily describe

methods for producing lithium hydroxide for embodying a technical idea of the present

invention, and the present invention does not specify the method for producing lithium

hydroxide to the following.

[0013]

The method for producing lithium hydroxide according to the present invention

includes the steps (1) to (5) below; (1) a hydrocarbonating step: a step of blowing

carbon dioxide to a slurry of a mixture of water and rough lithium carbonate to obtain a

lithium hydrogen carbonate solution; (2) a decarbonation step: a step of heating the

lithium hydrogen carbonate solution to obtain purified lithium carbonate; (3) an acid

solution dissolution step: a step of dissolving the purified lithium carbonate in an acid

solution to obtain a first lithium containing solution; (4) an impurity removal step: a

step of removing a part of metal ions from the first lithium containing solution to obtain

a second lithium containing solution; (5) a conversion step: a step of converting lithium

salt contained in the second lithium containing solution into lithium hydroxide by

electrodialysis to obtain a lithium hydroxide containing solution in which the lithium

hydroxide is dissolved.

[0014]

The present invention allows reliably removing metals other than lithium by

executing the hydrocarbonating step, the decarbonation step, and the acid solution

dissolution step in a step before the conversion step by electrodialysis, thereby allowing

an increased purity of obtained lithium hydroxide. Additionally, concentrations of

polyvalent metals with a valence of two or more, such as calcium, in an electrolyte can be lowered, thereby allowing a reduced damage of a barrier membrane used in the conversion step after these steps.

[0015]

In the method for producing lithium hydroxide, it is preferred to provide a

crystallization step of solidifying the lithium hydroxide dissolved in the lithium

hydroxide containing solution after the conversion step. This aspect allows solidifying

the lithium hydroxide to have a high purity using a difference in solubility.

[0016]

In the method for producing lithium hydroxide, it is preferred that the impurity

removal step includes a pH adjustment step of adjusting a pH by adding alkali into the

first lithium containing solution to obtain a post-pH adjustment liquid and an ion

exchange step of bringing the post-pH adjustment liquid into contact with ion-exchange

resin to obtain the second lithium containing solution. This aspect allows the pH to be

adjusted to be appropriate for the subsequent ion exchange step, and a removal rate of

divalent or more metals is substantially improved in the ion exchange step.

[0017]

removal step includes a step of adding an oxidant to the first lithium containing solution

to obtain a post-oxidation liquid, a pH adjustment step of adjusting a pH by adding

alkali into the post-oxidation liquid to obtain a post-pH adjustment liquid, and an ion

resin to obtain the second lithium containing solution. This aspect allows removing

manganese when the manganese is contained in the first lithium containing solution,

and allows pH to be adjusted to be appropriate for the subsequent ion exchange step in

the pH adjustment step, and a removal rate of divalent or more metals is substantially improved in the ion exchange step.

[0018]

In the method for producing lithium hydroxide, a pH of the post-pH adjustment

liquid after the pH adjustment step is preferred to be 6 or more and 10 or less. This

aspect allows removing impurities with more certainty in the ion exchange step after the

pH adjustment step.

[0019]

In the method for producing lithium hydroxide, the alkali used in the pH

adjustment step is preferred to be the purified lithium carbonate obtained in the

decarbonation step. This aspect allows avoiding impurities, such as sodium or

potassium, from being added. Additionally, since the product obtained from the

previous step is used, an extra cost can be saved.

[0020]

In the method for producing lithium hydroxide, in the decarbonation step, it is

preferred that the lithium hydrogen carbonate solution is heated at 60°C or more and

°C or less. This aspect allows shortening a process period in the decarbonation step.

[0021]

(First Embodiment)

Fig. 1 illustrates a flowchart of a method for producing lithium hydroxide

according to a first embodiment of the present invention. This embodiment executes (1)

a hydrocarbonating step, (2) a decarbonation step, (3) an acid solution dissolution step,

(4) an impurity removal step, and (5) conversion step in this order. In this embodiment,

the hydrocarbonating step is performed first. The hydrocarbonating step is a step of

blowing carbon dioxide to a slurry of a mixture of water and rough lithium carbonate to obtain a lithium hydrogen carbonate solution. Here, the "rough lithium carbonate" means one that contains lithium carbonate as a main component and has a high proportion of impurities compared with a "purified lithium carbonate" described later.

Specifically, lithium carbonate high in impurity obtained by the method disclosed in

the Mining Institute of Japan, Japan, 1984, volume 100 issue 1152, 115-122 from a

brine, such as a salt lake brine, a geothermal brine, and a petroleum brine, or a leaching

solution of lithium ore or the like corresponds to the "rough lithium carbonate."

[0022]

As shown in Formula 1, the rough lithium carbonate reacts with carbon dioxide

and water to be converted into lithium hydrogen carbonate high in solubility, and thus, a

lithium hydrogen carbonate solution is obtained. That is, the lithium hydrogen

carbonate melts into a liquid to turn into the lithium hydrogen carbonate solution, and

other sparingly soluble impurities solidifies. For example, this impurity is calcium

carbonate. Thus separating solid and liquid allows removing the calcium carbonate and

the like as the impurities.

[0023]

[Formula 1]

Li 2 CO 3 + CO2 + H2 0 -- 2LiHCO 3

[0024]

In the hydrocarbonating step according to the embodiment, the temperature is

preferred to be 20°C or more and 40°C or less. The blown carbon dioxide preferably

has an amount immediately before the unreacted and insoluble carbon dioxide starts to

come out in a form of air bubbles.

[0025]

As shown in Fig. 1 and Formula 2, in the decarbonation step, by heating the

lithium hydrogen carbonate solution, the lithium hydrogen carbonate is converted into

the purified lithium carbonate having a low solubility, and the purified lithium

carbonate is precipitated again to obtain the purified lithium carbonate. The rough

lithium carbonate contains a high concentration of sodium in some cases. Thus, to

reduce this sodium concentration, the lithium carbonate in the rough lithium carbonate

is dissolved as the lithium hydrogen carbonate having a high solubility in the

hydrocarbonating step. Afterwards, the lithium hydrogen carbonate is turned into

lithium carbonate again in a form of the purified lithium carbonate in the decarbonation

step to precipitate the purified lithium carbonate. Here, the "purified lithium carbonate"

means one that contains lithium carbonate as a main component and has a low

proportion of impurities compared with the "rough lithium carbonate" described above.

The sodium is almost removed from the precipitated purified lithium carbonate, and

thus, the purity of the purified lithium carbonate can be increased. The purified lithium

carbonate as the precipitate and the supernatant are separated into solid and liquid, thus

allowing obtaining the purified lithium carbonate as a solid material.

[0026]

[Formula 2]

2LiHCO 3 -- Li 2 CO 3 + CO2 + H2 0

[0027]

The decarbonation step according to the embodiment was performed at 80°C,

but it is not limited to this. For example, it is preferred to be performed at 60°C or more

and 90°C or less. This aspect allows shortening a process period in the decarbonation

step. The heating method is not particularly limited, and it is preferred to employ a method that corresponds to a scale of a reaction container. For example, a Teflon

(Registered Trademark) heater or steam heating can be employed. In the solid-liquid

separation in the decarbonation step according to the embodiment, it is preferred that a

filter press is used.

[0028]

As shown in Fig. 1, in the acid solution dissolution step, the purified lithium

carbonate obtained in the decarbonation step is dissolved with an acid solution to obtain

a lithium salt solution. The use of the lithium carbonate for the subsequent conversion

step causes two problems: the low solubility of the lithium carbonate allows only

conversion with thin liquid, and efficiency is poor (the size of facility becomes large

with respect to throughput); and carbonic acid gas is possibility generated during

conversion, possibly damaging the membrane. To solve these problems, the purified

lithium carbonate is dissolved with an acid solution to turn into a first lithium salt

solution as the lithium salt solution. Since the pH decreases after the acid solution

dissolution, adjusting the pH to the pH appropriate for impurity removal is preferred in

the ion exchange step. Note that the acid used in the acid solution dissolution step is

hydrochloric acid, sulfuric acid, nitric acid, and the like. Hydrochloric acid is used in

this embodiment, and a lithium chloride solution is obtained as a lithium salt solution in

the acid solution dissolution step. The chemical reaction formula is illustrated in

Formula 3.

[0029]

[Formula 3]

Li 2 CO 3 + 2HCl -- 2LiC1 + H 2 0 + CO 2

[0030]

Note that since the pH needs to be increased in the ion exchange step described

later, the amount of acid solution used in the acid solution dissolution step is preferably

the minimum necessary amount. For example, the pH is preferably adjusted to be 8.5.

[0031]

As shown in Fig. 1, in the impurity removal step, a part of metal ions is

removed from the first lithium containing solution to obtain a second lithium containing

solution. Fig. 2 illustrates a flowchart illustrating a configuration of the impurity

removal step according to the embodiment. In this embodiment, the impurity removal

step includes the pH adjustment step and the ion exchange step. Note that the impurity

removal step is not limited to the configuration illustrated here.

[0032]

As shown in Fig. 2, in the pH adjustment step, alkali is added to the first

lithium containing solution and a pH is adjusted to obtain a pH adjusted liquid. At this

time, depending on the adjustment pH or the impurity concentration, a pH adjustment

sediment containing some impurities is obtained. In the pH adjustment step, the post

pH adjustment liquid is adjusted to a pH appropriate for removing impurities, such as

Ca and Mg, in the ion exchange step subsequent to this. Specifically, the pH is

preferred to be 6 or more and 10 or less. When the pH is smaller than 6, the impurity

removal in the ion exchange step may be insufficient. When the pH is larger than 10, an

amount of added alkali is too much. The post-pH adjustment liquid is even more

preferred to be pH 7.5 or more and pH 8.5 or less. This is because an additive amount

of the neutralizer can be reduced and a necessary impurity removal performance can be

expected. The alkali is preferred to be one that does not contain sodium or potassium.

For example, the alkali is preferred to contain lithium carbonate or lithium hydroxide.

In this case, the lithium carbonate needs to be lithium carbonate with a 99% or more

purity, and the lithium hydroxide needs to be lithium hydroxide with a 99% or more

purity. Alternatively, this lithium carbonate is more preferred to be the purified lithium

carbonate obtained after undergoing the above-described decarbonation step. This

aspect allows avoiding the impurities, such as sodium or potassium, from being added.

Additionally, the use of the product obtained in the previous step allows saving an extra

cost.

[0033]

As shown in Fig. 2, in the ion exchange step, by bringing the post-pH

adjustment liquid into contact with the ion-exchange resin, a second lithium containing

solution from which a part of impurities has been removed is obtained. While in the ion

exchange step, divalent or more metal ions are removed, calcium, aluminum,

manganese, and magnesium by an amount of the solubility that remains corresponding

to the pH in the pH adjustment step are also removed at this time.

[0034]

Chelating resin is preferably used as the ion-exchange resin. For example,

iminodiacetic acid resin can be used. Specifically, Amberlite IRC748 can be used. A

preferred value is determined as the pH of the post-pH adjustment liquid in the ion

exchange step depending on the ion-exchange resin. Note that the ion exchange step is

preferably performed directly on the first lithium containing solution obtained in the

acid solution dissolution step. The method for contacting the ion-exchange resin and

the post-pH adjustment liquid is preferably a column method. However, there may be a

case where a batch mixing method is employed.

[0035]

As shown in Fig. 1, in the conversion step, lithium salt contained in the second

lithium containing solution is converted into lithium hydroxide to obtain a lithium

hydroxide containing solution in which lithium hydroxide is dissolved. In this

embodiment, the lithium salt is lithium chloride. In the second lithium containing

solution, the lithium salt is dissolved with the acid used in the acid solution dissolution

step in the impurity removal step. In this step, for example, an electrodialysis using a

bipolar membrane is performed to convert these aqueous solutions into the lithium

hydroxide containing solution containing lithium hydroxide and hydrochloric acid.

That is, by performing the electrodialysis, lithium chloride in the second lithium

containing solution is decomposed, lithium ions of lithium chloride pass through a

cation membrane and bind to hydroxide ions to become lithium hydroxide, and chloride

ions pass through an anion membrane to become hydrochloric acid. The recovered

hydrochloric acid can be recycled to the elution step. Accordingly, the usage of mineral

acid can be reduced.

[0036]

Note that, for example, an electrodialysis using an ion-exchange membrane

corresponds to the conversion step in addition to the electrodialysis using the bipolar

membrane. When a cation-exchange membrane is used as the ion-exchange membrane,

lithium hydroxide is generated in a cathode chamber.

[0037]

(Second Embodiment)

Fig. 3 depicts a flowchart of the impurity removal step of the method for

producing lithium hydroxide according to the second embodiment of the present

invention. This embodiment differs from the first embodiment in that the oxidation step is included before the pH adjustment step in the impurity removal step and is otherwise same as the first embodiment. The following describes the neutralization step according to the second embodiment.

[0038]

As shown in Fig. 3, the oxidation step is a step of adding an oxidant, such as

air, oxygen, and sodium hypochlorite, to the first lithium containing solution obtained in

the acid solution dissolution step to oxidize manganese in the first lithium containing

solution and obtain insoluble manganese dioxide, thereby precipitating to remove the

manganese dissolved in the liquid to obtain a post-oxidation liquid. While the

manganese is removable also in the above-described pH adjustment step, the manganese

is removed before the pH adjustment step by providing the oxidation step. Therefore,

the load of removing the manganese in the pH adjustment step can be reduced. The

manganese precipitated to be removed in the oxidation step is reusable. As the type of

the oxidant used in the oxidation step, air, oxygen, sodium hypochlorite, or the like can

be employed. The first lithium containing solution has a redox potential set to a pH and

an electric potential in a region of manganese dioxide in a Pourbaix diagram. The

obtained post-oxidation liquid is put to the pH adjustment step after the oxidation step.

[0039]

(Others)

In all of the embodiments, there may be a case where a crystallization step of

solidifying lithium hydroxide dissolved in the lithium hydroxide containing solution is

provided after the conversion step. The crystallization step is indicated by the dotted

line in Fig. 1.

[0040]

When the lithium hydroxide containing solution obtained in the conversion

step is evaporated to dryness, lithium hydroxide is obtained. However, this lithium

hydroxide containing solution contains alkali metals, such as sodium or potassium, and

the direct evaporation to dryness causes a solid material obtained from it to contain

much hydroxides other than lithium hydroxide. In view of this, the crystallization step

of solidifying lithium hydroxide dissolved in the lithium hydroxide containing solution

is preferably provided after the conversion step.

[0041]

In the crystallization step, by solidifying the lithium hydroxide dissolved in the

lithium hydroxide containing solution, a solid lithium hydroxide is obtained. A

crystallization mother liquor is obtained together with the solid lithium hydroxide. In

the conversion step, lithium becomes a lithium hydroxide, and the alkali metals, such as

sodium and potassium, become hydroxides. Accordingly, they are also contained in the

lithium hydroxide containing solution obtained in the conversion step. Furthermore,

chlorine ions as anions also pass through the membrane to be contained in the lithium

hydroxide containing solution. In the crystallization step, the difference in solubility

between the respective hydroxides is used to solidify the lithium hydroxide and separate

contained impurities.

[0042]

In the crystallization step, the lithium hydroxide containing solution is heated

to be concentrated. In this respect, the concentration of metal ions contained in the

liquid increases, and lithium hydroxide having a relatively low solubility is deposited

and solidified first. The deposited lithium hydroxide is recovered as the solid lithium

hydroxide. In this respect, sodium hydroxide or potassium hydroxide having relatively high solubility is not deposited and remains in the aqueous solution. Therefore, the purity of the recovered lithium hydroxide increases.

[0043]

For example, at 60°C, the solubility of lithium hydroxide is 13.2 g/100 g-water,

and it is seen that the solubility of lithium hydroxide is significantly low compared with

174 g/100 g-water of sodium hydroxide and 154 g/100 g-water of potassium hydroxide.

Since the chlorine ion is 2 g/L also during the operation of heating to concentrate, the

chlorine ion is not deposited as chloride of the alkali metal in the lithium hydroxide.

[0044]

This step can be industrially performed with a continuous crystallization using

a crystallization can. It can be performed also with a batch crystallization. The

crystallization mother liquor generated in the crystallization step is a concentrated

alkaline aqueous solution. Since the crystallization mother liquor contains lithium

hydroxide by an amount of the solubility, repeating the lithium adsorption step increases

a lithium recovery rate. In addition, the neutralizer cost decreases.

[Examples]

[0045]

The following will describe the specific examples of the method for producing

lithium hydroxide according to the present invention. However, the present invention is

not limited to the examples.

[0046]

(Example 1)

78 g of rough lithium carbonate and 1.56 L of pure water in Table 1 were put

into a plastic beaker of 2 L, and were stirred to be mixed to obtain a slurry. Carbon dioxide was blown to the slurry for three hours, and the unreacted and insoluble carbon dioxide started to come out in a form of air bubbles. With this blowing of carbon dioxide, the lithium carbonate was converted into lithium hydrogen carbonate and was dissolved. This hydrocarbonating step was performed at 30°C. In the hydrocarbonating step, after the blowing of carbon dioxide, the slurry was suctioned and the residue was removed, and the lithium hydrogen carbonate solution in Table 2 was obtained.

[0047]

[Table 1]

K Li Mg Na C Coined metal B a

<10 <10 17000 100 17 30 <10 23000 15000

[0048]

[Table 2]

Cnandmtl Al B Ca K Li Mg Mn Na Contained metal g/L g/L g/L g/L g/L gL g/L g/L <0.0I <O.00I 0.005 0.006 7.400 0009 <O.0 1.200

[0049]

1.56 L of the lithium hydrogen carbonate solution obtained in the

hydrocarbonating step was put into a stainless-steel beaker of 2 L, was, while being

heated to 80°C, stirred to be mixed for approximately 3 hours. In view of this, the

lithium hydrogen carbonate was converted into lithium carbonate and precipitated. The

obtained purified lithium carbonate was cleaned by repulping and watering with pure

water, and dried by heating. After drying by heating, 46 g of the purified lithium

carbonate was obtained. Analysis values thereof are shown in Table 3.

[0050]

[Table 3]

ea Cotie metal Contamned Al' B Ca K ILi Mg Mn Na IC1 pp. ppm ppm pp- ppm ppm ppm ppm <10 <10 120 <20 19 58 <10 80 <50

[0051]

By comparing Table 1 and Table 3, it was found that the decarbonation step

could reduce the impurities. That is, it was found that impurity concentrations of

sodium, calcium, and magnesium were reduced.

[0052]

70 g of purified lithium carbonate obtained in the decarbonation step and 400

ml of pure water were put into a plastic beaker of 1 L, and were stirred to be mixed to

obtain a slurry. 165 ml of 37% HCl was added to the slurry, and pure water was added

so as to obtain 700 ml of the first lithium containing solution.

[0053]

The purified lithium carbonate obtained in the above-described decarbonation

step was added to the first lithium containing solution obtained in the acid solution

dissolution step, and a pH was adjusted to remove impurities in the ion exchange step.

In this embodiment, the stirring and mixing was performed to obtain pH of 8.4, and a

post-pH adjustment liquid was obtained. This step was all performed at ordinary

temperature. Contained metals as the impurities are shown in Table 4. It is seen that

the content of sodium is significantly reduced by undergoing the decarbonation step, the

acid solution dissolution step, and the pH adjustment step.

[0054]

[Table 4]

Cnandmtl Al -B Ca K Li Mg Mn Na Contained metal g/L g/L g1L g!L gIL g/L gIL g/L <0.001 <0.001 0.004 0.003 21.400 0.002 <0.001 0.009

[0055]

20 ml of chelating resin (Amberlite: IRC748 manufactured by Du Pont) was

filled in a glass column, and was conditioned to make it a functional group Li type.

Afterwards, just 600 mL (BV30) of the post-pH adjustment liquid obtained in the pH

adjustment step was passed through the column at a liquid passing rate of 1.67 ml/min

(SV5). Table 5 shows a metal concentration of the second lithium containing solution

after flowing out of the column. It is seen that this ion exchange step could reduce

calcium and magnesium to an extremely small amount.

[0056]

[Table 5]

Ca K Li Mg Mn Na Contained metal Al B g/L g/L g/L g/L g/L g/L g/L g/L <0.001 <0.001 <0.00005 0.004 19.000 <0.00005 <0.001 0.008

[0057]

1 L of the second lithium containing solution obtained in the impurity removal

step was introduced to a bipolar membrane electrodialysis unit (manufactured by

ASTOM Corporation: ACILYZER EX3B), and lithium chloride was converted into

lithium hydroxide. A liquid amount of the lithium hydroxide containing solution after the conversion was 0.6 L. Fig. 4 illustrates a relation between an energizing time and a lithium concentration in the lithium hydroxide containing solution. The lithium concentration in the lithium hydroxide containing solution increased along with the energization, and was concentrated to 28 g/L to 29 g/L in the end. Table 6 shows a metal concentration after the electrodialysis. As can be seen in the table, it is seen that a high purity lithium hydroxide containing solution with a very low impurity concentration was obtained.

[0058]

[Table 6]

Contained metal A IC K L M g/L g/L~ g/L F)L g/L g/L Ig/L Ig/L g/L <0.001 <0.001 <0.001 0.008 27,000 <0.001 <0.001 0.039 2.100

[0059]

0.6 L of the lithium hydroxide containing solution obtained in the conversion

step was put into a stainless-steel beaker, was heated while being stirred and kept at a

temperature of 90°C to 100°C, was concentrated to 0.2 L, and a deposited lithium

hydroxide crystal was recovered. Table 7 shows analysis values of this lithium

hydroxide crystal. It is seen that the lithium hydroxide crystal with a low impurity

concentration could be recovered.

[0060]

[Table 7]

K Li Mg Mn Na Cl Contained metal Al B Ca ppm ppm ppm ppm % ppm ppm ppm ppm <10 <10 <10 <20 19 <10 <10 <10 <50

[0061]

(Comparative Example 1)

The difference between Comparative Example 1 and Example 1 is that the

decarbonation step was not performed in the steps of Example 1. Other than this,

Comparative Example 1was all performed under the same conditions. That is, the

lithium hydrogen carbonate solution obtained in the hydrocarbonating step was directly

added with hydrochloric acid to perform the acid solution dissolution step, and

thereafter, a lithium hydroxide containing solution was obtained through the impurity

removal step and the conversion step. The result is shown in Table 8. Compared with

Table 6, it is seen that a significantly high concentration of sodium is contained.

[0062]

[Table 8]

Al B Ca K Li Mg Mn Na Contained metal g/L g/L g/L g/L g/L g/L g/L g/L <0,001 <0001 0001 0.090 27.000 <0.001 <0001 3,400

Claims

What is claimed is:

1. A method for producing lithium hydroxide comprising steps (1) to (5) below:

(1) a hydrocarbonating step of blowing carbon dioxide to a slurry of a mixture

of water and rough lithium carbonate to obtain a lithium hydrogen carbonate solution;

(2) a decarbonation step of heating the lithium hydrogen carbonate solution to

obtain a purified lithium carbonate;

(3) an acid solution dissolution step of dissolving the purified lithium carbonate

in an acid solution to obtain a first lithium containing solution;

(4) an impurity removal step of removing a part of metal ions from the first

lithium containing solution to obtain a second lithium containing solution; and

(5) a conversion step of converting lithium salt contained in the second lithium

containing solution into lithium hydroxide by electrodialysis to obtain a lithium

hydroxide containing solution in which the lithium hydroxide is dissolved.

2. The method for producing lithium hydroxide according to claim 1, comprising

a crystallization step of solidifying the lithium hydroxide dissolved in the

lithium hydroxide containing solution after the conversion step.

3. The method for producing lithium hydroxide according to claim 1 or 2,

wherein

the impurity removal step includes:

a pH adjustment step of adjusting a pH by adding alkali to the first

lithium containing solution to obtain a post-pH adjustment liquid; and

an ion exchange step of bringing the post-pH adjustment liquid into

contact with ion-exchange resin to obtain the second lithium containing solution.

4. The method for producing lithium hydroxide according to claim 1 or 2,

wherein

the impurity removal step includes:

a step of adding an oxidant to the first lithium containing solution to

obtain a post-oxidation liquid;

a pH adjustment step of adjusting a pH by adding alkali into the post

oxidation liquid to obtain a post-pH adjustment liquid; and

an ion exchange step of bringing the post-pH adjustment liquid into

5. The method for producing lithium hydroxide according to claim 3 or 4,

wherein

the pH of the post-pH adjustment liquid after the pH adjustment step is 6 or

more and 10 or less.

6. The method for producing lithium hydroxide according to any one of claims 3

to 5, wherein

the alkali includes lithium carbonate or lithium hydroxide.

7. The method for producing lithium hydroxide according to claim 6, wherein

the lithium carbonate is the purified lithium carbonate obtained in the

decarbonation step.

8. The method for producing lithium hydroxide according to any one of claims 1 to 7, wherein in the decarbonation step, the lithium hydrogen carbonate solution is heated at

°C or more and 90°C or less.